1. Field of the Invention
The invention relates to powder-filled tube and to a method for the continuous manufacture of such tube. The invention is particularly but not exclusively applicable to powder-filled tube known as ladle wire which is used in metallurgical processes, and to powder-filled tube used as, or in the manufacture of, welded rod.
2. Description of the Prior Art
Powder-filled tube having a steel outer wall welded to form a closed tube and a compacted powder core in the closed tube is well known. Various methods, none of them wholly satisfactory, for manufacturing such tube have been proposed.
In GB-A-No. 1,604,144 and EP-A-No. 3370 methods are described for the continuous fabrication of a welded tube filled with powder, starting from a strip of metal which is formed into an open channel, into which filler powder is fed. In this condition the edges of the channel are brought together and held together by pressure after which a closed longitudinal seam is created by electric welding. Afterwards the diameter of the closed tube is reduced so that the powder filler within the tube is substantially compressed and thereby cannot shift during further handling. This method has the practical difficulty that the nature of the powder can negatively influence the quality of the weld made can contaminate the edges of the strip through the magnetic ingredients in the powder. At the same time there are limitations on the filling ratio (the weight ratio between the quantity of powder and the quantity of steel per unit length). Also there are limits to the production rates achievable.
U.S. Pat. No. 3,543,381 shows a process in which a strip is formed into a channel, the channel is filled and then the channel edges are brought together to form a butt seam or a lapped seam. The seam is not welded. Compaction of the powder is poor, and the powder may leak or be contaminated because the seam is not an adequate seal. DE-A-No. 2,603,412 similarly described the production of a filled tube with a lapped, non-welded seam, but in this case the powder is first compacted into a wire-shape before being inserted into the tube.